To determine factors responsible for irreversible cardiac failure, hemodynamic studies were performed in 11 dogs with circulatory overload (secondary to aorto-caval shunt) and again late after reversal of the shunt. The magnitude of the shunt is a reliable predictor of residual left ventricular dilatation. However, usually employed hemodynamic indices of cardiac function are of little value in predicting potential for reversibility of cardiac failure.